Magnetic position sensors find application in a number of industrial fields including especially automobiles. In automobiles, magnetic position sensors are employed to detect crankshaft position and the like. They comprise a permanent magnet, a moving ferromagnetic target and a magnetic field sensor. The ferromagnetic target moving through the field of the permanent magnet causes a modulation of the magnetic field in the region of the magnetic field sensor. The varying magnetic field is detected and is used as a basis for determining the position of some component to which the moving target may be affixed.
Many applications of magnetic position sensors use the modulation of the magnetic field component that is normal to the plane of the magnetic sensor. Conventional Hall sensors and semiconductor magnetoresistors are suitable for such applications because these sensors are responsive to the normal magnetic field component. However, there are some applications in which the geometrical application of the sensor would favor the use of a magnetic sensor, which is sensitive to modulation of the magnetic field component in the plane of the magnetic sensor. In these applications, of course, conventional Hall sensors and present semiconductor film magnetoresistors are unsuitable.
Publications by David J. Bergman et al over the period of 1994 through 1996 first predicted and then demonstrated that inhomogeneities in a conductive film such as a periodic array of small cylindrical voids (antidots) embedded in a thin film of n-doped GaAs caused a pronounced anisotropy of magnetoresistance. In the Bergman et al work where the magnetic field lies in the plane of the GaAs film, a resistivity dependence on the angle between the in-plane magnetic field and an electrical current passed through the film was observed. In the experimental portion of the work, which was reported in Bergman et al, Phys. Rev. Lett., 77, 147 (1996), the observed magnetoresistance anisotropy effect was observed at a low temperature, 90 K, and a very strong magnetic field, B&gt;4 Tesla.
It would now be desirable to devise a sensitive galvanomagnetic device that would be useful at normal room temperature and over the temperature range found in automotive applications, for example. Furthermore, it would be useful to adapt such a device to provide useful information in a magnetic position sensor combination.